Mainoru Station in central Arnhem Land has teamed up with a research group to rehydrate its flood plains after years of being dry due to erosion.
Through the construction of what’s known as “leaky weirs”, the Mainoru team has been working hard to bring water back into the environment.
The team on the station, located almost 300 kilometres east of Katherine near the Central Arnhem Highway in the Northern Territory, musters cattle on the 137,000-hectare property.
Danny Hayes and Lance Mugway walk through the dry flood plain full of the weed known as greater grass. (ABC Rural: Jan Kohout)
Erosion causing dry flood plains
The cattle and buffalo station relies heavily on its grass-rich flood plains to feed its cattle, which had slowly been filled by a detrimental weed called “greater grass”.
Mainoru Station owner Danny Hayes said the greater grass had left cattle and buffalo with little to feed on.
Buffalo roaming the relatively dryer than usual flood plains at Mainoru Station. (ABC Rural: Jan Kohout)
“It’s become an issue because I can’t feed greater grass to my cattle and for the environment, it’s not letting any other grass species grow,” Mr Hayes said.
“I’m trying to rehydrate those flood plains to let better species of grass to grow and stop erosion deepening my river creek systems.
“Greater grass hates having wet feet, so if I can rehydrate my country and get the water to lay there four to six weeks, I hope some other grass species that supports water logging can start to grow.”
Mainoru River channel erosion has caused the flood plain above to go dry. (ABC Rural: Jan Kohout)
Mainoru has a flood plain area that has three main river channels passing through it.
The three major channels have been eroded into deep gullies three metres deep on average instead of flowing across the plains.
Building weirs made from local resources
Mulloon Institute hydrologist and landscape planner Lance Mugway has travelled across the Northern Territory advising cattle stations about rehydrating and managing their waterways.
He said one way to change the course of the water was to build a “leaky weir” which banks the water up slowly but leaks at the same time.
Leaky weirs look similar to weirs, except they are made up of odd, shaped stones and debris found in the waterways that allow the water to leak out slowly.
Leaky weirs look similar to weirs except that they are made up of odd, shaped stones and debris. (ABC Rural: Jan Kohout)
“The floodwaters have come down to stay in those channels and they don’t flood out onto the flood plains and have effectively been dehydrated,” Mr Mugway said.
“One way to fix that is by raising up those channels again, so the floodwater goes back onto the flood plain.
“We need to use material that is at hand because it’s hard to bring in any material from town, that is far too expensive.
“In the case of Mainoru, we have a supply of rock, some of it is good rock. It’s blocky, angular and shaped nicely to form a structure with.
“We can also use logs, debris and heavy branches that are at hand in the environment.”
Leaky weirs also create a natural step in the water level that helps rebuild the creek from erosion with sediments.
Having water flowing upstream can allow sediments to settle and start building a creek back up.
Lance Mugway and Danny Hayes on top of the old weir that was built by the station’s previous owners. (ABC Rural: Jan Kohout)
Mr Mugway said there was no such thing as putting too much water into these flood plains.
“We’ve lost so much water into these systems due to that erosion process, therefore, we are trying to recapture the water that has been stored in the landscape previous to white men coming along,” he said.
“From seeing how much floodwater comes along every wet season, we will be banking only five to 10 per cent of it.”
Mr Hayes said he was rebuilding on top of the previous leaky weir built a long time ago by the previous owners.
“I have started but it’s mainly stuff that has already been done and I’m just repairing on top of the previous build,” he said.
“It’s slowly working but I made a lot of mistakes, hence why I’ve been coming to Lance Mugway to find out how to do it properly.”
Erosion eating away at cattle stations
Erosion in northern Australia is caused by high rain season flows and dryer conditions.
Darryll Hill, who was a cattleman in the Victoria River Daly District of the Northern Territory and now runs an erosion awareness workshop, said he has seen the effects of land loss on pastoral properties.
Darryll Hill pictured (third left) teaching a group at one of his Soil Save workshops.
(Facebook: Soil Save)
“Degradation of the roads can lead to insecure fencing, maintenance and cost of vehicles, travelling time, paddock security as well,” he said.
“There is unfortunately a fair cost involved but it’s hard to put a dollar figure on it.
“If it takes three days to grade a paddock fence line when it should only take one day then there are two days of grader work lost.”
Mr Hill said an estimated 600 million tonnes of soil was lost in rivers every year across Australia.
He also said erosion costs the economy $600 million a year.
Mr Hill said erosion was a natural phenomenon that happened worldwide that hampers development.
“Our rivers and creeks are natural, however, what is not natural is the soil loss happening on properties,” he said.
“It’s been estimated years ago that 75 per cent of soil loss on properties is off access tracks and roads.”
